This invention relates to apparatus for and methods of bonding a component to a substrate. More particularly, this invention relates to apparatus for and methods of removing small components, such a dies or other electrical components, from a wafer and bonding the components to a substrate.
In the production of electronic circuitry, particularly circuitry containing semiconductor chips or dice, there is a need for extremely rapid and accurate placement of the chip or die on a substrate. In many applications a plurality of chips to be placed on the substrate are removably held upon a thin film prior to being placed on the substrate. Each chip must be removed or extracted from the thin film and rapidly transferred to the substrate. In some applications, the chip is only placed on the substrate while in other applications it may be held on the substrate by an adhesive which may also serve as an electrical connection, heat sink, or both. The chips may be of various sizes and configurations and they must be placed on the substrate at precise locations to an accuracy of a few thousandths of an inch.
Rapid production of high quality chip/substrate assemblies requires a precision apparatus which incorporates effective quality control features. For example, in order to remove the chip from the wafer without damage, it is required that the chip is precisely aligned to the tool or tools which will remove it. It is also necessary that the interaction between the removing tool or tools and the chip is not so violent so as to cause damage to the chip. Effective quality control also requires that substandard or defective chips be detected and passed by so that the production or sale of a defective chip/substrate assembly is avoided. It is also required that the tool or tools which place the chip upon the substrate do not do so with such violence so as to cause damage to the chip or the substrate. This is particularly true when complex function chips or very large chips are being bonded to the substrate by the application of epoxy or some other adhesive. The prior art has satisfied the above listed needs only partially.
Prior art devices generally place the wafer or other component holding device in substantially the same plane as the substrate. Assembly of the chip to the substrate proceeds in assembly-line fashion wherein a pick up head moves along a relatively long horizontal axis between a pickup station and a placement station. This arrangement often requires that the pick up head be movable over long distances and in several directions. For example, see U.S. Pat. No. 3,958,740--Dixon in which the pick up head is movable along a horizontal axis, a vertical axis, and is rotatable about the vertical axis. This arrangement not only requires complex and bulky pick up head assemblies, but also limits the capacity of the apparatus by making the distance through which the head assembly travels a function of the size of the wafer and/or the substrate. That is, as the substrate and/or wafer size increase, the distance the head must travel to pickup the die and place it on the substrate will also generally increase. Thus, the time required to produce each assembly is increased. This is especially important in light of current trend in the industry toward larger and larger wafers.
Other prior art applications employ carousel type devices having several stations located along the path of a rotary member as disclosed in U.S. Pat. No. 3,946,931--Bahnck et al. Devices of this type have the disadvantage of requiring separate and independent stations for the several functions required of a bonding apparatus. That is, a device of this type consists of a substrate loading station, a substrate aligning station, a tack bonding station, a substrate monitoring station, a final bonding station, a second monitoring station, and a substrate unloading station. As a result, devices of this type tend to be large and relatively slow. In addition, devices of this type also hold the wafer and the substrate on substantially the same plane. As a result, the distance the bond head must travel will generally increase as the size of the wafer and/or the substrate increases.
As already mentioned, a device which produces an unnecessarily large force on the chip during the transfer process can damage or destroy the chip or the resulting chip/substrate assembly and thereby reduce the effective capacity of the apparatus. On the other hand, a device which does not utilize sufficient removal or placement force when transferring the chip from the wafer to the substrate can cause missed pickups or poorly bonded chips. Thus, the ability to regulate or adjust the pickup and/or placement force according to the dictates of the particular application would increase apparatus efficiency and thereby improve productivity. In addition, the advantage of providing an adjustable tool for reducing violent chip/substrate interaction may become more important in the future. This is so because Gallium Arsenide (GaAs) chips, which are relatively fragile, are potentially the "chip of the future". See for example SMTRENDS, Volume 2, No. 12, page 3, column 3. The prior art, however, has used pickup and placement techniques which provide little or no ability to adjust the pickup and placement force. For example, the devices disclosed in U.S. Pat. Nos. 4,166,562--Keizer et al and 4,500,032--Ackerman both utilize spring loaded actuating means for unloading and loading the chip. U.S. Pat. No. 3,946,931--Bahnck et al. discloses the use of a mechanical lever arm for removal and placement of the chip. None of the these devices permit ready adjustment.